Power operated rotary knives have been used in commercial meat processing operations to trim fat and connective tissue from meat, trim pieces of meat from bones, and to produce meat slices. Such knives are often constructed so that they are driven via a long flexible drive shaft. The knife operator wields the knife relatively freely at a meat cutting work station that is remote from the driving motor.
These power operated knives represented a major improvement over use of hand knives or knives having an integral drive motor. Knife operator fatigue was greatly reduced, enabling both increased productivity and greater knife operator comfort. Nevertheless knife operator fatigue was not eliminated. Some knives incorporated “take-with” handles that were sized to fit the hands of knife operators using the knives. These handles could be removed from the knives and taken with the knife operator after using the knife. Take-with handles reduced fatigue because the knife operator could always use a knife with a handle that was properly sized. The handles were difficult to install in proper alignment with the knife blade.
Some previously known rotary knives were provided with steeling mechanisms. But these were not convenient to use because the knife operator had to significantly reposition the knife hand or use two hands to steel the blade.
When the blades of rotary knives must be replaced, the blade is removed from its housing on the knife. In many prior art knives, removing the blade was difficult and required the blade housing to be semi-detached from the knife in order for the blade to be removed and replaced. This required significant operator time and skill to achieve because the blade housing and associated parts had to be properly aligned for the knife to perform optimally. In other knives a special blade removal mechanism was incorporated in the knife. This increased the knife weight and added to the cost of the knives so equipped.
The drive connection between the flexible drive shaft and the blade rotating gearing was typically formed by a square cross section flex shaft end that plugged into a square opening in a drive gear. The blade drive was disconnected by pulling the flex shaft end out of the drive gear opening. The resultant engagement forces between the faces of the flex shaft end and gear opening had force components that were radially directed as well as normal to the radial components. The normal force components were effective to transmit torque and were of smaller magnitude than the respective engagement forces. Therefore, for a given amount of torque transmission, the frictional forces resisting disconnection were great because the frictional forces were proportional to the engagement force. This tended toward increased difficulty in disconnecting the blade drive.